The maintenance of spermatozoa outside the body of man and animals is customarily carried out in artificial insemination procedures. There are a variety of materials and procedures which are used in the prior art to prolong the survival of spermatozoa outside the body and/or to enable a single sperm-containing ejaculate to be diluted so as to be useful to impregnate a large number of females. Many of these materials and procedures are limited as to the extent they can prolong survival. Materials more complex than the ordinary balance solutions are commonly referred to as "extenders."
There is a particular problem with prolonging the survival of porcine spermatozoa. In many cases, the survival of washed porcine sperm is limited to only 2 to 4 hours at physiological conditions. Attempts to freeze porcine sperm by conventional techniques have been relatively unsuccessful. Often recovery of less than 20% of motility of the spermatozoa is obtained. Glycerol which is often considered essential for successful freezing of bovine spermatozoa can be highly toxic to porcine boar sperm.
The admixture of either washed or unwashed porcine spermatozoa with any of a variety of commercially available extenders usually results in two dramatic effects. After only a few hours the sperm show progressively decreasing motility. In addition, they agglutinate or clump to one another or to the particulate material normally present in seminal fluid and which is difficult to remove from the spermatozoa by filtration or differential centrifugation.
Often extenders used for extending porcine spermatozoa, are only effective to allow the seminal plasma of boars to be diluted as with egg yolk. Thus an ejaculate from a boar can be extended by some commercial extenders to allow 6 to 8 sows to be inseminated. However, the life of the sperm is often not extended by commercially available extenders. Thus often in many species, commercial extenders don't extend the life span of the spermatozoa but only permit survival of diluted sperm equivalent to those of undiluted sperm.
It has long been recognized that it would be useful to have an extender which extends both the fertility and motility of pig and other sperm while allowing dilution of the sperm to a high degree to enable a single ejaculate to be used for insemination of an increased number of sows.